Method of producing precision tapered tubes

ABSTRACT

A tapered metal tube is formed slightly undersize, stretched over a mandrel of precisely finished size, annealed on the mandrel and cooled, then again heated while the mandrel is cooled to facilitate removal.

United States Patent Wightman [451 Apr. 24, 1973 [5 METHOD OF PRODUCING PRECISION [56] References Cited TAPERED TUBES UNITED STATES PATENTS [75] Inventor: Lawrance W. Wightman, Saint 2 302 22 11/194 Lam t 48/12 p on Lows County 1,378,639 5/1921 Warner [73] Assignee: Emerson Electric Co., St. Louis, Mo.

a. Primary Examiner-Lowell A. Larson [22] led: 1971 AttorneyCharles E. Markham [21] A No.: 127 448 v pp 57 ABSTRACT [52] U S Cl 72/364 72/370 A tapered metal tube is formed slightly undersize, 51] d 31/00 stretched over a mandrel of precisely finished size, an- 5 Fieid 364 370 nealed on the mandrel and cooled, then again heated 72/701; 29/DIG. 41; 148/12, 131

while the mandrel is cooled to facilitate removal.

5 Claims, 4 Drawing Figures P'ATENIED m 24 1015 METHOD OF PRODUCING PRECISION TAPERED TUBES This invention relates to a method of mass producing flared or tapered metal tubes having precisely uniform internal dimensions and configuration.

It is difficult by conventional methods to mass produce flared or tapered metal tubes to the close tolerances required for their interchangeable use in certain devices such as, for example, in flowmeters. Usually, it is necessary to calibrate each tube separately to achieve the desired accuracy in flowmeter readings. The calibration of each tube considerably increases the cost of the flowmeter, so that the provision ofa method of producing precisely uniform interchangeable tapered tubes will result in a substantial reduction in cost.

It is therefore the primary object of this invention to provide a method of mass producing tapered metal tubes having precisely uniform internal configuration and dimensions.

A further object is to provide a method of mass producing precisely uniform tapered metal tubes which are entirely free of internal stresses.

Other objects and advantages will appear from the following complete description of the method and apparatus when read in connection with the accompanying drawing.

FIG. 1 is a side elevational view of a round tube, con structed in accordance with the method of invention, having an intermediate tapered portion and cylindrical end portions, being of the type conventionally employed in flowmeters;

FIG. 2 is a longitudinal cross-sectional view of the tube in FIG. 1 in its slightly undersize form, shown on a forming mandrel;

FIG. 3 is a longitudinal crosssectional view of the tube of FIG. 1 in its finished size form, shown on a sizing mandrel; and

FIG. 4 is a side elevational view ofa configured tube constructed in accordance with the method of invention having a flared intermediate portion, the walls of which are curved longitudinally.

As a first step in the method of constructing the metal tube of FIG. 1, a metal tube having a tapered or flared portion of substantially the desired configuration, but slightly under the desired diametral size of the finished tube, is constructed by any suitable means. For example, the tube with an undersize tapered portion may be formed by swaging a cylindrical metal tube of suitable size on a forming mandrel having a tapered portion 12 slightly less diametrally than the desired inside diameter of the finished tube.

As a second step in the method, the undersize tube is stretched over a sizing mandrel 14 in FIG. 3, having a slightly larger tapered portion 16. The undersize tube may be stretched over the sizing mandrel 14 by pressing it on, or by expanding the tube sufficiently by heating it to permit insertion of the sizing mandrel, or by partially expanding the tube by heating and partially by pressing it on the sizing mandrel 14.

The sizing mandrel 14 has a tapered portion 16 of precisely the form and diametral size of the inside of the finished tube and is constructed of a metal having the same coefficient of expansion as that of the tube material. The degree of stretching of the undersize tube over the tapered surface of the sizin mandrel 14, by whatever means, must be sufficient o insure that the entire interior surface of the tapered portion of the tube is in contact with the tapered surface of the sizing mandrel and under some substantial stress at normal ambient atmospheric temperatures.

As a third step in the method, the sizing mandrel with the tube thereon is heated suitably to the annealing temperature of the tube for a suitable period of time and then cooled to atmospheric temperature to effect removal of all internal stresses in the tube at normal atmospheric temperature arising from forming or stretching.

As a fourth step in the method, the tube is again heated relatively rapidly while the sizing mandrel is cooled, thereby to facilitate removal of the tube from the sizing mandrel. The tube may be heated rapidly by immersion of the tube and mandrel in a hot bath while the mandrel is cooled by passing a fluid coolant through the longitudinal passage 18 therein. The ends of the passage 18 are screw threaded to receive conduits for conducting coolant through the mandrel 14.

When certain metals are used for construction of the tube, it is not necessary to cool the sizing mandrel below atmospheric temperature, but only to heat the tube rapidly to facilitate its removal.

It will be understood that the cylindrical end portions 20 and 22 of the sizing mandrel 14 are substantially the same diameter as the cylindrical end portions of the forming mandrel, there being no provision for precisely sizing cylindrical end portions of this length. Relatively short cylindrical end portions may, however, be sized in a manner similar to the tapered portion.

lclaim:

l. The method of producing a tapered metal tube of precise internal taper and diametral dimensions which consists in forming a tapered metal tube in which the internal surface is tapered substantially as desired in the finished tube but is undersize diametrally, in stretching the undersize metal tube over a tapered sizing mandrel having precisely the taper and diametral dimensions desired for the internal surface of the finished tube, the tube being stretched sufficiently to I stress it substantially and the sizing mandrel being constructed of a material having substantially the same coefficient of expansion as the material of the tube, in heating the sizing mandrel with the stretched tube thereon to the annealing temperature of the tube at a suitable rate and for a suitable period of time and in cooling the tube and mandrel to atmospheric temperature at a suitable rate to effect removal of internal stresses in the tube, and in reheating the tube sufficiently to facilitate its removal from the sizing mandrel.

2. The method set forth in claim 1 in which the mandrel is cooled while the tube is heated in the last step to facilitate removal ofthe tube.

3. The method set forth in claim 1 in which the undersize tapered tube is heat stretched over the sizing mandrel.

4. The method set forth in claim 1 in which the undersize tube is pressed on the sizing mandrel.

5. The method set forth in claim 1 in which the undersize tube is stretched over the sizing mandrel par tially by heating and partially by pressing. 

1. The method of producing a tapered metal tube of precise internal taper and diametral dimensions which consists in forming a tapered metal tube in which the internal surface is tapered substantially as desired in the finished tube but is undersize diametrally, in stretching the undersize metal tube over a tapered sizing mandrel having precisely the taper and diametral dimensions desired for the internal surface of the finished tube, the tube being stretched sufficiently to stress it substantially and the sizing mandrel being constructed of a material having substantially the same coefficient of expansion as the material of the tube, in heating the sizing mandrel with the stretched tube thereon to the annealing temperature of the tube at a suitable rate and for a suitable period of time and in cooling the tube and mandrel to atmospheric temperature at a suitable rate to effect removal of internal stresses in the tube, and in reheating the tube sufficiently to facilitate its removal from the sizing mandrel.
 2. The method set forth in claim 1 in which the mandrel is cooled while the tube is heated in the last step to facilitate removal of the tube.
 3. The method set forth in claim 1 in which the undersize tapered tube is heat stretched over the sizing mandrel.
 4. The method set forth in claim 1 in which the undersize tube is pressed on the sizing mandrel.
 5. The method set forth in claim 1 in which the undersize tube is stretched over the sizing mandrel partially by heating and partially by pressing. 